The candidate is a well-trained molecular biologist and biochemist with greater than four years of postdoctoral research experience in cell signaling, virology, and hematopoietic stem cell (HSC) biology. He is committed to a career in biological research, with the immediate goal of attaining independence and funding in his research program. The candidate's long-term career goal is to establish a niche in the hematopoietic stem cell field where he can be at the forefront of basic science research in HSC self-renewal. The objective of this KO1 proposal is to define of the role of core binding factor (CBF) in self-renewal and differentiation of HSC. Core binding factor is a heterodimeric transcription factor complex comprised of a DNA-binding subunit, RUNX1, and a non- DNA-binding subunit, CBFbeta. The absence of either subunit in mice results in embryonic lethality and the complete absence of definitive hematopoietic cells. Expression of a dominant inhibitor of CBF activity, AML1-ETO, in adult HSC resulted in a 30-fold expansion of HSC in vivo, which suggests that CBF regulates genes that are necessary for HSC self-renewal and function. To define the role of CBF in HSC self-renewal, the following specific aims will be pursued: (1) define the roles of RUNX1 and CBFb in adult HSC and hematopoiesis using RNA interference to knock-down their expression in HSC of transplanted mice, (2) determine the effects of CBFb-MYH 11 expression on maintenance and self-renewal of HSC, (3) functionally quantitate the increased self-renewing capacity of HSC that express AML1-ETO, and (4) functionally map the regions within the ETO domain of AML1-ETO that are responsible for HSC expansion. The completion of these aims will provide new insight into the molecular control of HSC self-renewal and could provide insight into a means of expanding human HSC in vitro. This would have direct clinical application in the areas of transplantation, hematopoietic gene therapy, and potential therapies of non-hematopoietic tissues.